The Phylogenetic Significance of the Feather Character 'Flexules'

Abstract

The taxonomic distribution of 'flexules', structures found in the pennaceous part of contour feathers of certain birds, was studied with light- and scanning electron microscopy. Observations by earlier workers are extended and the phylogenetic significance and functional aspects of these structures are evaluated. Aspects of homology between flexules and other barbicels, such as claw-like projections ('Krallen' = 'ungules'), tooth-like projections ('Zinkenfortsatze' = 'denticules'), and villi, are discussed. The presence of flexules is postulated as a phylogenetically old synapomorphy, defining a group of mainly aquatic birds.